Image sensors

ABSTRACT

An image sensor includes a device isolation layer disposed in a substrate and defining pixel regions, and a grid pattern on a surface of the substrate. The grid pattern overlaps the device isolation layer between adjacent pixel regions in a direction perpendicular to the surface. The grid pattern has a width less than a width of the device isolation layer.

CROSS-REFERENCE TO RELATED APPLICATION

A claim for priority under 35 U.S.C. §119 is made to Korean PatentApplication 10-2016-0100033 filed on Aug. 5, 2016, the disclosure ofwhich is incorporated herein in its entirety by reference.

BACKGROUND

The present inventive concepts relate to image sensors and, moreparticularly, to complementary metal oxide semiconductor (CMOS) imagesensors.

Image sensors are semiconductor devices that transform light of opticalimages into electrical signals. Recent advances in computer andcommunication industries have led to increased demand for highperformance image sensors for use in various consumer electronic devicessuch as digital cameras, camcorders, PCSs (Personal CommunicationSystems), game devices, security cameras, medical micro cameras, or thelike. Accordingly, there currently exists an increasing need to enhanceperformance of image capturing devices or image sensors included inimage capturing devices.

SUMMARY

Embodiments of the inventive concept provide an image sensor havingenhanced sensitivity characteristics.

Embodiments of the inventive concept provide an image sensor including adevice isolation layer disposed in a substrate and defining pixelregions; and a grid pattern over a surface of the substrate. The gridpattern overlaps the device isolation layer between adjacent pixelregions in a first direction perpendicular to the surface. The gridpattern has a width less than a width of the device isolation layer.

Embodiments of the inventive concept provide an image sensor including adevice isolation layer disposed in a substrate and defining pixelregions; photoelectric conversion devices respectively on the pixelregions in the substrate; and a grid pattern over a surface of thesubstrate and overlapping the device isolation layer in a firstdirection perpendicular to the surface. The grid pattern is be spacedapart from at least one of the photoelectric conversion devices along asecond direction perpindicular to the first direction.

Embodiments of the inventive concept further provide an image sensorincluding a substrate having an array of photoelectric conversiondevices in respective pixel regions defined by a device isolation layerwithin the substrate. The device isolation layer has a lattice shape.The image sensor further includes a grid pattern over a surface of thesubstrate. The grid pattern has a lattice shape and overlaps the deviceisolation layer to partly cover the device isolation layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an image sensor according toembodiments of the inventive concept.

FIG. 2 illustrates a circuit diagram of an active pixel sensor array ofan image sensor according to embodiments of the inventive concept.

FIG. 3 illustrates a circuit diagram of an active pixel sensor array ofan image sensor according to embodiments of the inventive concept.

FIG. 4 illustrates a plan view of an active pixel sensor array accordingto embodiments of the inventive concept.

FIG. 5 illustrates a cross-sectional view taken along line I-I′ of FIG.4, showing an active pixel sensor array according to embodiments of theinventive concept.

FIG. 6 illustrates an enlarged view of section A in FIG. 5, showing agrid pattern according to embodiments of the inventive concept.

FIG. 7A to 7D illustrate cross-sectional view descriptive of a method offorming a grid pattern discussed with reference to FIGS. 4 to 5.

FIG. 8 illustrates an enlarged view of section A in FIG. 5, showing agrid pattern according to other embodiments of the inventive concept.

FIG. 9 illustrates a cross-sectional view taken along line I-I′ of FIG.4, illustrating an active pixel sensor array according to otherembodiments of the inventive concept.

FIG. 10 illustrates an enlarged view of section B in FIG. 9.

FIG. 11 illustrates a cross-sectional view taken along line I-I′ of FIG.4, illustrating an active pixel sensor array according to otherembodiments of the inventive concept.

DETAILED DESCRIPTION OF EMBODIMENTS

As is traditional in the field of the inventive concepts, embodimentsmay be described and illustrated in terms of blocks which carry out adescribed function or functions. These blocks, which may be referred toherein as units or modules or the like, are physically implemented byanalog and/or digital circuits such as logic gates, integrated circuits,microprocessors, microcontrollers, memory circuits, passive electroniccomponents, active electronic components, optical components, hardwiredcircuits and the like, and may optionally be driven by firmware and/orsoftware. The circuits may, for example, be embodied in one or moresemiconductor chips, or on substrate supports such as printed circuitboards and the like. The circuits constituting a block may beimplemented by dedicated hardware, or by a processor (e.g., one or moreprogrammed microprocessors and associated circuitry), or by acombination of dedicated hardware to perform some functions of the blockand a processor to perform other functions of the block. Each block ofthe embodiments may be physically separated into two or more interactingand discrete blocks without departing from the scope of the inventiveconcepts. Likewise, the blocks of the embodiments may be physicallycombined into more complex blocks without departing from the scope ofthe inventive concepts.

FIG. 1 illustrates a block diagram of an image sensor according toembodiments of the inventive concept.

Referring to FIG. 1, an image sensor 10 includes an active pixel sensorarray (APS) 1, a row decoder 2, a row driver 3, a column decoder 4, atiming generator 5, a correlated double sampler (CDS) 6, ananalog-to-digital converter (ADC) 7, and an input/output (I/O) buffer 8which are variously interconnected by wiring or the like (not shown).

The active pixel sensor array 1 may include a plurality oftwo-dimensionally arranged unit pixels, each of which is configured toconvert optical signals into electrical signals. The active pixel sensorarray 1 may be driven by a plurality of driving signals such as a pixelselect signal, a reset signal, and a charge transfer signal providedfrom the row driver 3. The converted electrical signals may be providedfrom the active pixel sensor array 1 to the correlated double sampler 6.

In some embodiments of the inventive concept, the image sensor 10 mayperform an auto focusing operation via phase difference detection oflight incident onto the active pixel sensor array 1. Each of the unitpixels of the active pixel sensor array 1 may output a focus signalcorresponding to phase difference of light incident onto a pair ofphotoelectric conversion devices. To perform the auto focusingoperation, the focus signal may be used as a signal to adjust lenspositions of an image capturing device including the image sensor 10.

The row driver 3 may provide the active pixel sensor array 1 withseveral driving signals for driving several unit pixels in accordancewith a decoded result obtained from the row decoder 2. In the case thatthe unit pixels are arranged in a matrix shape, the driving signals maybe supplied to respective rows.

The timing generator 5 may provide timing and control signals to the rowdecoder 2 and the column decoder 4.

The correlated double sampler 6 may receive the electrical signalsgenerated in the active pixel sensor array 1, and hold and sample thereceived electrical signals. The correlated double sampler 6 may performa double sampling operation to sample a specific noise level and asignal level of the electrical signal, and then output a differencelevel corresponding to a difference between the noise and signal levels.

The analog-to-digital converter 7 may convert analog signals, whichcorrespond to the difference level received from the correlated doublesampler 6, into digital signals, and then output the converted digitalsignals.

The input/output buffer 8 may latch the digital signals and thensequentially output the latched digital signals to an image signalprocessing unit (not shown) in response to the decoded result obtainedfrom the column decoder 4.

FIG. 2 illustrates a circuit diagram of an active pixel sensor array 1of an image sensor according to embodiments of the inventive concept.

Referring to FIG. 2, the active pixel sensor array 1 may include aplurality of unit pixel regions P that are two-dimensionally arrangedalong rows and columns. Incident light may be converted into electricalsignals at each of the unit pixel regions P, and the unit pixel regionsP may be driven by driving signals transmitted through a pixel selectline SEL, a charge transfer line Tx, and a reset line Rx that areconnected to the unit pixel regions P. The electrical signals convertedat the unit pixel regions P may be provided to a control circuit (notshown) through output lines Vout.

FIG. 3 illustrates a circuit diagram of an active pixel sensor array 1of an image sensor according to embodiments of the inventive concept.

Referring to FIG. 3, the active pixel sensor array 1 may include theplurality of unit pixel regions P, which may be arranged in a matrixshape along row and column directions. Each of the unit pixel regions Pmay include first and second photoelectric conversion devices PD1 andPD2, transfer transistors TX1 and TX2, and logic transistors RX, SX andDX. The logic transistors RX, SX and DX may include a reset transistorRX, a select transistor SX, and a drive transistor or source followertransistor DX. Gate electrodes of the first transfer transistors TX1,the second transfer transistor TX2, the reset transistor RX, and theselect transistor SX may be connected to a corresponding one of drivingsignal lines TG1, TG2, RG and SG. The driving signal lines TG1 and TG2may be hereinafter referred to as a first transfer gate TG1 and a secondtransfer gate TG2. The driving signal lines TG1 and TG2 may correspondto the charge transfer line Tx shown in FIG. 2, the driving signal lineRG may correspond to the reset line Rx shown in FIG. 2, and the drivingsignal line SG may correspond to the pixel select line SEL shown in FIG.2. The driving signal lines RG and SG may hereinafter be respectivelyreferred to as the reset signal line RG and the pixel select line SG.

The first transfer transistor TX1 may include the first transfer gateTG1 and the first photoelectric conversion device PD1, and the secondtransfer transistor TX2 may include the second transfer gate TG2 and thesecond photoelectric conversion device PD2. The first and secondtransfer transistors TX1 and TX2 are connected to and share a chargedetect node FD (i.e., a floating diffusion region).

The first and second photoelectric conversion devices PD1 and PD2 maygenerate and accumulate photo-charges in proportion to an amount oflight incident from external. The first and second photoelectricconversion devices PD1 and PD2 may be one of for example a photo diode,a photo transistor, a photo gate, a pinned photo diode (PPD), and anycombination thereof. The first photoelectric conversion device PD1 isconnected between ground and the first transfer transistor TX1, and thesecond photoelectric conversion device PD2 is connected between groundand the second transfer transistor TX2.

The first and second transfer transistors TX1 and TX2 may respectivelytransfer the charges which are accumulated in the first and secondphotoelectric conversion devices PD1 and PD2 to the charge detect nodeFD (i.e., the floating diffusion region), responsive to charge transfersignals provided to the first and second transfer gates TG1 and TG2. Thefirst and second transfer gates TG1 and TG2 may receive complementarycharge transfer signals. In other words, the charges may be transferredto the charge detect node FD from one of the first and secondphotoelectric conversion devices PD1 and PD2 at a time.

The charge detect node FD may receive and accumulatively store thecharges generated from the first and second photoelectric conversiondevices PD1 and PD2. The drive transistor DX may be controlled by anamount of photo-charges accumulated in the charge detect node FD.

The reset transistor RX may periodically reset the charges accumulatedin the charge detect node FD. In detail, the reset transistor RX mayhave a drain electrode connected to the charge detect node FD and asource electrode connected to a power supply voltage VDD. When the resettransistor RX is turned on responsive to a reset signal on the resetline RG, the charge detect node FD may receive the power supply voltageVDD connected to the source electrode of the reset transistor RX.Accordingly, when the reset transistor RX is turned on, the chargesaccumulated in the charge detect node FD may be exhausted and thus thecharge detect node FD may be reset.

In conjunction with a static current source (not shown) located outsidethe unit pixel regions P, the drive transistor DX may serve as a sourcefollower buffer amplifier. The drive transistor DX may amplify avariation in electrical potential of the charge detect node FD andoutput the amplified electrical potential to an output line Vout.

The select transistor SX may select each row of the unit pixel regions Pto be read. When the select transistor SX is turned on responsive to apixel select signal on the pixel select line SG, the power supplyvoltage VDD connected to the drain electrode of the drive transistor DXmay be transmitted to a drain electrode of the select transistor SX.

FIG. 4 illustrates a plan view of an active pixel sensor array 1according to embodiments of the inventive concept. FIG. 5 illustrates across-sectional view taken along line I-I′ of FIG. 4, showing an activepixel sensor array 1 according to embodiments of the inventive concept.In this description, a direction vertical to a substrate 100 (orperpendicular to planar upper or lower (main) surfaces of substrate 100)may be defined as a y-direction, and a horizontal directionperpendicular to the first direction may be defined as an x-direction,as shown in FIG. 5. The y-direction and the x-direction may hereinafterbe respectively referred to as the first direction and the seconddirection. FIG. 5 shows the active pixel sensor array 1 a as one exampleof the active pixel sensor array 1 of FIG. 4.

Referring to FIGS. 4 and 5, the substrate 100 may include a firstsurface 100 a and a second surface 100 b facing each other. For example,the first surface 100 a may be a front surface of the substrate 100 andthe second surface 100 b may be a rear surface of the substrate 100.Circuits may be disposed on the first surface 100 a, and light may beincident onto the second surface 100 b. The substrate 100 may forexample be a silicon substrate doped with a first conductive impurity,for example an n-type impurity. In other embodiments of the inventiveconcept, substrate 100 may for example be one of a germanium substrate,a silicon-germanium substrate, a Group II-VI compound substrate, a GroupIII-V compound substrate, and an SOI (Silicon On Insulator) substrate.In some embodiments, the first conductive impurity may have aconcentration that decreases approaching the second surface 100 b fromthe first surface 100 a of the substrate 100.

The substrate 100 may include a first device isolation layer 102 and aplurality of pixel regions P defined by the first device isolation layer102. The first device isolation layer 102 may vertically extend alongthe first direction from the first surface 100 a to the second surface100 b of the substrate 100. The first device isolation layer 102 mayhave a vertical thickness substantially the same as that of thesubstrate 100. In plan view, the first device isolation layer 102 mayhave a lattice shape. The first device isolation layer 102 may bereferred to as a deep trench isolation (DTI) layer formed in thesubstrate 100. The first device isolation layer 102 may be formed of aninsulative material having a refractive index less than that of thesubstrate 100 (e.g., silicon). For example, the first device isolationlayer 102 may include silicon oxide. As shown in FIG. 5, the firstdevice isolation layer 102 may have a substantially uniform width alongthe first direction. In some embodiments of the inventive concept, thefirst device layer 102 may have a width that decreases approaching thesecond surface 100 b from the first surface 100 a of the substrate 100.Also, although not shown in the figures, in some embodiments the firstdevice isolation layer 102 may include a plurality of liners orinsulation layers.

In some embodiments of the inventive concept, photo-charges may begenerated in proportion to intensity of light incident onto the pixelregions P. For example, the entirety of the pixel regions P defined bythe first device isolation layer 102 may generate the photo-chargesproportional to the intensity of incident light. The first deviceisolation layer 102 may refract an obliquely incident light L, such thatthe pixel regions P may not receive incident light L obliquely incidentonto neighboring pixel regions P. That is, the device isolation layer102 may prevent a pixel region P from receiving light that is obliquelyincident on a neighboring pixel region P. As the first device isolationlayer 102 penetrates the substrate 100, adjacent pixel regions P may becompletely separated from each other. In this configuration,photo-charges generated from the substrate 100, onto which light isincident, of each pixel region P may be prevented from randomly driftingto neighboring pixel regions P.

A photoelectric conversion device PD may be disposed in the substrate100 of each pixel region P. The photoelectric conversion device PD maybe disposed spaced apart from the first surface 100 a of the substrate100. The photoelectric conversion device PD may be, for example, ann-type impurity doped region. A well region 107 may be disposed on thepixel region P of the substrate 100. The well region 107 may be disposedadjacent to the first surface 100 a of the substrate 100. A depth fromthe first surface 100 a to the well region 107 may be less than a depthof the first device isolation layer 102 from the first surface 100 a.The well region 107 may be, for example, a p-type impurity doped region.

In some embodiments, first and second active zones ACT1 and ACT2 may bedefined by a second device isolation layer 105, which may be disposedadjacent to the first surface 100 a of the substrate 100. The seconddevice isolation layer 105 may be disposed in the well region 107 anddefine the first and second active zones ACT1 and ACT2 on each of pixelregions P. The first and second active zones ACT1 and ACT2 may be aportion of the well region 107. The first and second active zone ACT1and ACT2 may be disposed spaced apart from each other on each of thepixel regions P. The first and second active zones ACT1 and ACT2 mayhave sizes and shapes different from each other. In some embodiments, asshown in FIG. 4, in plan view each of the second active zones ACT2 onadjacent pixel regions P may be disposed between the first active zonesACT1 on the adjacent pixel regions P.

In some embodiments, for example, a transfer gate TG and a floatingdiffusion region FD may be disposed on the first active zone ACT1 in thesubstrate 100 of each of the pixel regions P. The floating diffusionregion FD may be disposed closely adjacent to the first surface 100 a ofthe substrate 100. The floating diffusion region FD may be a dopedregion whose conductivity is opposite to that of the well region 107.The floating diffusion region FD may be, for example, an n-type impuritydoped region. The transfer gate TG may be disposed on the first surface100 a of the substrate 100. The transfer gate TG may be disposed on eachof the pixel regions P. In some embodiments, the transfer gate TG may bedisposed as neighboring or next to the floating diffusion region FD.

Logic transistors may be disposed on the second active zones ACT2 of thepixel regions P. For example, the logic transistors may be one of areset transistor RX, a source follower (drive) transistor DX, and aselect transistor SX such as shown in FIG. 3. Two adjacent pixel regionsP may share the logic transistors.

An interconnect line structure 110 may be disposed on the first surface100 a of the substrate 100. The interconnect line structure 110 mayinclude the logic transistors, interconnect lines 113 connected to thelogic transistors, and contact plugs 115. Interlayer dielectric layers111 a, 111 b and 111 c may be disposed stacked on the first surface 100a of the substrate 100, and may cover the transfer gate TG. A pluralityof contact plugs 115 and a plurality of interconnect lines 113 may bedisposed in the interlayer dielectric layers 111 a, 111 b and 111 c. Thecontact plugs 115 may electrically connect the logic transistors to thefloating diffusion region FD.

Color filters C/F and micro lenses 140 may be disposed on or over thesecond surface 100 b of the substrate 100. An antireflection layer 120may be disposed between the color filters C/F and the second surface 100b of the substrate 100. The antireflection layer 120 may completelycover the second device isolation layer 105. The antireflection layer120 may prevent light reflection such that the photoelectric conversionregion PD may be allowed to readily receive light incident onto thesecond surface 100 b of the substrate 100.

The color filters C/F and the micro lenses 140 may be disposed tocorrespond to the pixel regions P. The color filters C/F may include oneof red, green, and blue filters depending on a unit pixel. The colorfilters C/F may be two-dimensionally arranged. Alternatively, the colorfilters C/F may include yellow, magenta, and cyan filters. The colorfilters C/F may further include a white filter.

The micro lens 140 may have a convex shape and a predetermined curvatureradius. The micro lens 140 may be formed of a light-transmissive resinand may condense incident light onto each pixel region P.

A grid pattern 130 may be disposed on the antireflection layer 120. Inmore detail, the grid pattern 130 may be disposed on or over the secondsurface 100 b of the substrate 100 and between adjacent color filtersC/F. The grid pattern 130 may overlap the first device isolation layer102 between adjacent pixel regions P in the first direction. That is,the grid pattern 130 may extend over the first device isolation layer102 so as to partly cover the first device isolation layer 102. In planview, the grid pattern 130 may have a lattice shape. In plan view, thegrid pattern 130 may be spaced apart from at least one of its adjacentphotoelectric conversion devices PD along (or in) the second direction.In plan view, at least a portion of the first device isolation layer 102may be exposed between the grid pattern 130 and the spaced one of thephotoelectric conversion devices PD. That is, there is at least aportion of the first isolation layer 102 that is between the gridpattern 130 and one of the photoelectric conversion devices PD, and theat least one portion is not overlapped or covered by the grid pattern130. The grid pattern 130 may reflect the light L obliquely incidentonto the second surface 100 b of the substrate 100 to allow the pixelregions P to receive corresponding reflected light L.

FIG. 6 illustrates an enlarged view of section A in FIG. 5, showing agrid pattern 130 a according to embodiments of the inventive concept.Referring to FIG. 6, the grid pattern 130 a may include a lower grid 132a and an upper grid 134 a that are sequentially stacked. The upper grid134 a may be an upper portion of the grid pattern 130 a, and the lowergrid 132 a may be a lower portion of the grid pattern 130 a. The lowerand upper grids 132 a and 134 a may include different kinds of metalsfrom each other. For example, the upper grid 134 a may include tungsten(W), and the lower grid 132 a may include titanium nitride (TiN),although in other embodiments the upper and lower grids 132 a and 134 amay be other materials. The lower grid 132 a may contact the upper grid134 a to the antireflection layer 120.

The grid pattern 130 a may have a substantially uniform width or asubstantially non-uniform width along the first direction. For example,the lower and upper grids 132 a and 134 a may have widths different fromeach other. The upper grid 134 a may have a first width Wg1, and thelower grid 132 a may have a second width Wg2. The first width Wg1 may besubstantially uniform along the first direction. The second width Wg2may be greater than or equal to the first width Wg1. For example, thesecond width Wg2 of the lower grid 132 a may gradually increaseapproaching the substrate 100 from the upper grid 134 a. The secondwidth Wg2 may be a maximum allowed width of the lower grid 132 a. Thegrid pattern 130 a may thus have a width Wg, which may correspond to amaximum allowed width (e.g., the second width Wg2) of the lower grid 132a. Although FIG. 6 shows that the second width Wg2 is greater than thefirst width Wg1, in other embodiments the second width Wg2 may besubstantially the same as the first width Wg1.

The width Wg of the grid pattern 130 a may be less than a width Wd ofthe first device isolation layer 102. For example, the width Wg of thegrid pattern 130 a may be about 100 nm or less. As such, in plan viewthe first device isolation layer 102 may surround opposite sides of thegrid pattern 130 a. Although FIG. 6 shows that the first deviceisolation layer 102 has the uniform width Wd along the first direction,in other embodiments of the inventive concept the first device isolationlayer 102 may have a non-uniform width along the first direction. Inthis case, the width Wd of the first device isolation layer 102 may be aminimum allowable width of the first device isolation layer 102.

The grid pattern 130 a may have a height Hg less than a height Hc ofeach of the color filters C/F. For example, the height Hg of the gridpattern 130 a may be equal to or less than half the height Hc of each ofthe color filters C/F. The upper grid 134 a may have a height greaterthan that of the lower grid 132 a. For example, the height of the uppergrid 134 a may be about 1 to 5 times the height of the lower grid 132 a.

According embodiments of the inventive concept, the grid pattern 130 amay reflect the obliquely incident light L1 so that the pixel region Pmay receive corresponding reflected light L1′. An amount of lightincident onto corresponding pixel region P may increase as the width Wgand the height Hg of the grid pattern 130 a decreases, thereby enhancingsensitivity and SNR (signal-to-noise ratio). Differently from theembodiments of the inventive concept, if the width of the grid patternis greater than the width of the first device isolation layer or thegrid pattern is spaced apart from the first device isolation layer inplan view, an optical dead zone may be formed in the substrate 100overlapped with the grid pattern in the first direction. An amount oflight incident onto the pixel regions P may therefore decrease due tothe optical dead zone. In addition, if the height of the grid pattern isgreater than half the height of the color filters, the grid pattern mayreceive increased amount of incident light, so that loss of incidentlight may occur. For example, a portion of light incident onto the gridpattern may be reflected to travel into the pixel region P, whileanother portion of light may be lost due to its transmission through thegrid pattern.

FIGS. 7A, 7B, 7C and 7D illustrate cross-sectional views descriptive ofa method of forming a grid pattern 130 discussed with reference to FIGS.4 to 6.

Referring to FIG. 7A, a first metal layer 131, a second metal layer 133,a hardmask layer 150, and a photomask pattern 162 may be formed on asecond surface 100 b of a substrate 100. An interconnect line structure110 may be formed on a first surface 100 a of the substrate 100. In aneffort to simplify the drawings, antireflection layer 120 shown in FIG.5 and various internal structural features in the substrate 100 and theinterconnect line structure 110 as shown in FIG. 5, are omitted fromFIGS. 7A-7D. The internal structural features may have already beenformed in the substrate 100 and the interconnect line structure 110shown in FIGS. 7A-7D.

In more detail, the first metal layer 131 and the second metal layer 133may be sequentially formed on or over the second surface 100 b of thesubstrate 100. The first and second metal layers 131 and 133 may includedifferent metals and/or alloys from each other. For example, the firstmetal layer 131 may include titanium nitride (TiN) and the second metallayer 133 may include tungsten (W), although in other embodiments firstand second metal layers 131 and 133 may be formed of other metals oralloys. The second metal layer 133 may adhere the first metal layer 131to the substrate 100.

The hardmask layer 150 may be formed on the second metal layer 133. Forexample, the hardmask layer 150 may be an spin on hardmask (SOH) layer.The photomask pattern 162 may be formed on the hardmask layer 150. Thephotomask pattern 162 may be formed by coating a photomask layer (notshown) and then patterning the photomask layer. As not shown in figures,an insulation layer (e.g., a low temperature oxide layer) may beadditionally formed between the hardmask layer 150 and the photomaskpattern 162.

Referring to FIG. 7B, a hardmask pattern 152 may be formed by etchingthe hardmask layer 150 using the photomask pattern 162 as an etchingmask. For example, the hardmask layer 150 may be dry etched. Anashing/strip process may be performed to subsequently remove thephotomask pattern 162.

Referring to FIG. 7C, a grid pattern 130 may be formed by etching thefirst and second metal layers 131 and 133 using the hardmask pattern 152as an etching mask. The first and second metal layers 131 and 133 maybe, for example, dry etched. An ashing/strip process may be performed tosubsequently remove the hardmask pattern 152.

Referring to FIG. 7D, as shown in FIG. 5, a color filter C/F and a microlens 140 may be formed on the substrate 100 and the grid pattern 130 ofeach of pixel regions P.

According to such method of fabricating an image sensor, an etchingprocess may be performed using the hardmask layer 150 so that the gridpattern 130 may be formed to have a finely uniform width along the firstdirection. For example, the grid pattern 130 may have a width of about100 nm or less.

FIG. 8 illustrates an enlarged view of section A in FIG. 5, showing agrid pattern 130 b according to other embodiments of the inventiveconcept. Referring to FIG. 8, the grid pattern 130 b may be provided toinclude a single grid 132 b. The grid 132 b may be formed of a singlemetal or alloy. For example, the grid 132 b may be formed of titanium(Ti) or titanium nitride (TiN), although in other embodiments grid 132 bmay be formed of other metals or alloys. The grid pattern 130 b may havea width Wg that is substantially uniform along the first direction andless than a width Wd of the first device isolation layer 102 formed inthe substrate 100. With regard to FIG. 8, the description of elementsand configuration substantially the same as in FIG. 6 are omitted.

FIG. 9 illustrates a cross-sectional view taken along line I-I′ of FIG.4, showing an active pixel sensor array 1 b according to otherembodiments of the inventive concept. FIG. 10 illustrates an enlargedview of section B in FIG. 9. In the discussion of the active pixelsensor array 1 b, components substantially the same as those of theactive pixel sensor array 1 a described with reference to FIGS. 4 to 6are allocated the same reference numerals thereto, and repetitiveexplanations may be omitted for brevity.

The active pixel sensor array 1 b may further include a refractive fence150. The refractive fence 150 may be disposed on a grid pattern 130 c.Each of the color filters C/F may have a buried shape between adjacentstacking structures. Each of the stacking structures includes the gridpattern 130 c and the refractive fence 150 that are stacked one atop theother. The refractive fence 150 may have a refractive index less thanthat of the grid pattern 130 c. For example, the refractive index of therefractive fence 150 may be about 1.3 or less. The refractive fence 150may include oxide, but in other embodiments may be other materials.

The refractive fence 150 may have a height Hf equal to or greater than aheight Hg of the grid pattern 130 c. For example, the height Hf of therefractive fence 150 may be equal to or greater than half the height Hcof each of the color filters C/F. The refractive fence 150 may have awidth Wf equal to or greater than a width Wg of the grid pattern 130 c.The width Wf of the refractive fence 150 may be equal to or less thanthe width Wg of the first device isolation layer 102. The refractivefence 150 may totally reflect an obliquely incident light L2 so that thetotally reflected light L2′ may be incident into a corresponding one ofthe pixel regions P. An amount of light incident onto the correspondingpixel region P may thus be increased so that image sensor 1 b may haveenhanced sensitivity.

FIG. 11 illustrates a cross-sectional view taken along line I-I′ of FIG.4, showing an active pixel sensor array 1 c according to embodiments ofthe inventive concept. In the discussion of the active pixel sensorarray 1 c, components substantially the same as those of the activepixel sensor array 1 a described with reference to FIGS. 4 to 6 areallocated the same reference numerals thereto, and repetitiveexplanations may be omitted for brevity.

The active pixel sensor array 1 c may further include a protectiveplanarization layer 170 between the color filters C/F and the secondsurface 100 b of the substrate 100. The protective planarization layer170 may be a highly doped impurity layer. For example, the protectiveplanarization layer 170 may be doped with p-type impurity such as boron(B). The grid pattern 130 may be disposed in the protectiveplanarization layer 170. The grid pattern 130 in the active pixel sensorarray 1 c may be one of the aforementioned grid patterns 130 a, 130 band 130 c.

According to embodiments of the inventive concept, an etching processmay be performed using the hardmask layer so that the grid pattern maybe formed to have a finely uniform width. As the grid pattern has thefinely uniform width, the pixel region may receive an increased amountof incident light such that sensitivity and SNR (signal-to-noise ratio)of the image sensor may be enhanced.

The effects of the embodiments of the inventive concept are not limitedto the aforementioned effects. Other effects, not mentioned above,should be apparent and understood by one skilled in the art from theforegoing description and accompanying drawings.

These embodiments herein are presented to facilitate understanding ofthe present inventive concept and should not limit the scope of theinventive concept, and it is intended that the inventive concept coversthe various combinations, modifications, and variations of the disclosedembodiments. The scope of the inventive concept should be defined by thetechnical spirit of the appended claims, and is intended to include allmodifications and equivalents substantially falling within the spiritand scope of the inventive concept while not being limited by literarydescriptions in the appended claims.

What is claimed is:
 1. An image sensor, comprising: a device isolationlayer disposed in a substrate and defining pixel regions; and a gridpattern over a surface of the substrate, wherein the grid patternoverlaps the device isolation layer between adjacent pixel regions in afirst direction perpendicular to the surface, the grid pattern having awidth less than a width of the device isolation layer.
 2. The imagesensor of claim 1, wherein the width of the grid pattern issubstantially uniform along the first direction.
 3. The image sensor ofclaim 1, further comprising photoelectric conversion devicesrespectively over the pixel regions in the substrate, wherein the gridpattern is spaced apart from at least one of the photoelectricconversion devices along a second direction perpendicular to the firstdirection.
 4. The image sensor of claim 3, wherein at least a portion ofthe device isolation layer is exposed between the grid pattern and theat least one of the photoelectric conversion devices.
 5. The imagesensor of claim 1, further comprising color filters disposed over thesurface of the substrate and respectively provided over the pixelregions, wherein the grid pattern is disposed between adjacent colorfilters from among the color filters, the grid pattern having a heightequal to or less than half a height of each of the color filters.
 6. Theimage sensor of claim 1, wherein the grid pattern comprises a lowergrid, and an upper grid on the lower grid, the upper grid having a widthsubstantially uniform along the first direction.
 7. The image sensor ofclaim 6, wherein the lower grid has a width greater than or equal to thewidth of the upper grid.
 8. The image sensor of claim 1, furthercomprising a refractive fence on the grid pattern, wherein therefractive fence has a refractive index less than a refractive index ofthe grid pattern.
 9. The image sensor of claim 8, wherein the refractivefence has a height greater than or equal to a height of the gridpattern.
 10. The image sensor of claim 8, wherein the refractive fencehas a width greater than or equal to the width of the grid pattern. 11.The image sensor of claim 1, wherein the width of the grid pattern isabout 100 nm or less.
 12. The image sensor of claim 1, furthercomprising: color filters disposed over the surface of the substrate andrespectively provided over the pixel regions; and a planarization layerbetween the substrate and the color filter, wherein the grid pattern isdisposed in the planarization layer.
 13. An image sensor, comprising: adevice isolation layer disposed in a substrate and defining pixelregions; photoelectric conversion devices respectively over the pixelregions in the substrate; and a grid pattern over a surface of thesubstrate and overlapping the device isolation layer in a firstdirection perpendicular to the surface, wherein the grid pattern isspaced apart from at least one of the photoelectric conversion devicesalong a second direction perpendicular to the first direction.
 14. Theimage sensor of claim 13, wherein at least a portion of the deviceisolation layer is exposed between the grid pattern and the at least oneof the photoelectric conversion devices.
 15. The image sensor of claim13, wherein the grid pattern has a width substantially uniform along thefirst direction, the width of the grid pattern being less than a widthof the device isolation layer.
 16. An image sensor, comprising: asubstrate comprising an array of photoelectric conversion devices inrespective pixel regions defined by a device isolation layer within thesubstrate, the device isolation layer having a lattice shape; and a gridpattern over a surface of the substrate, the grid pattern having alattice shape and overlapping the device isolation layer to partly coverthe device isolation layer.
 17. The image sensor of claim 16, wherein awidth of the grid pattern is less than a width of the device isolationlayer.
 18. The image sensor of claim 16, further comprising colorfilters disposed over the surface of the substrate and respectivelyprovided over the pixel regions, wherein the grid pattern is disposedbetween adjacent color filters from among the color filters, the gridpattern having a height equal to or less than half a height of each ofthe color filters.
 19. The image sensor of claim 16, further comprisinga refractive fence on the grid pattern, the refractive fence having arefractive index less than a refractive index of the grid pattern. 20.The image sensor of claim 19, wherein a width of the refractive index isgreater than a width of the grid pattern.